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2017-12-11Merge branches 'cond_resched.2017.12.04a', 'dyntick.2017.11.28a', ↵Paul E. McKenney1-1/+2
'fixes.2017.12.11a', 'srbd.2017.12.05a' and 'torture.2017.12.11a' into HEAD cond_resched.2017.12.04a: Convert cond_resched_rcu_qs() to cond_resched() dyntick.2017.11.28a: Make RCU dynticks handle interrupts from NMI fixes.2017.12.11a: Miscellaneous fixes srbd.2017.12.05a: Remove now-redundant smp_read_barrier_depends() torture.2017.12.11a: Torture-testing update
2017-12-05doc: De-emphasize smp_read_barrier_dependsPaul E. McKenney1-1/+2
This commit keeps only the historical and low-level discussion of smp_read_barrier_depends(). Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com> [ paulmck: Adjusted to allow for David Howells feedback on prior commit. ]
2017-12-04doc: Eliminate cond_resched_rcu_qs() in favor of cond_resched()Paul E. McKenney1-2/+2
Now that cond_resched() also provides RCU quiescent states when needed, it can be used in place of cond_resched_rcu_qs(). This commit therefore documents this change. Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
2017-08-17doc: Set down RCU's scheduling-clock-interrupt needsPaul E. McKenney1-0/+130
This commit documents the situations in which RCU needs the scheduling-clock interrupt to be enabled, along with the consequences of failing to meet RCU's needs in this area. Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
2017-06-09rcu: Remove debugfs tracingPaul E. McKenney1-1/+1
RCU's debugfs tracing used to be the only reasonable low-level debug information available, but ftrace and event tracing has since surpassed the RCU debugfs level of usefulness. This commit therefore removes RCU's debugfs tracing. Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
2017-06-09rcu: Remove SPARSE_RCU_POINTER Kconfig optionPaul E. McKenney1-6/+3
The sparse-based checking for non-RCU accesses to RCU-protected pointers has been around for a very long time, and it is now the only type of sparse-based checking that is optional. This commit therefore makes it unconditional. Reported-by: Ingo Molnar <mingo@kernel.org> Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com> Cc: Fengguang Wu <fengguang.wu@intel.com>
2017-06-09rcu: Remove nohz_full full-system-idle state machinePaul E. McKenney1-5/+1
The NO_HZ_FULL_SYSIDLE full-system-idle capability was added in 2013 by commit 0edd1b1784cb ("nohz_full: Add full-system-idle state machine"), but has not been used. This commit therefore removes it. If it turns out to be needed later, this commit can always be reverted. Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com> Cc: Frederic Weisbecker <fweisbec@gmail.com> Cc: Rik van Riel <riel@redhat.com> Cc: Ingo Molnar <mingo@kernel.org> Acked-by: Linus Torvalds <torvalds@linux-foundation.org>
2017-06-08doc: Take tail recursion into account in RCU requirementsPaul E. McKenney1-1/+2
This commit classifies tail recursion as an alternative way to write a loop, with similar limitations. Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
2017-06-08srcu: Document auto-expediting requirementPaul E. McKenney1-0/+14
This commit documents the auto-expediting requirement satisfied by commits 2da4b2a7fd8d ("srcu: Expedite first synchronize_srcu() when idle") and 22607d66bbc3 ("srcu: Specify auto-expedite holdoff time"). Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
2017-04-12doc: Update requirements based on recent changesPaul E. McKenney1-26/+94
These changes include lighter-weight expedited grace periods, the fact that expedited grace periods and rcu_barrier() no longer block CPU hotplug, some HTML font fixups, noting that rcu_barrier() need not wait for a grace period (even if callbacks are posted), the fact that SRCU read-side critical sections can be used from offline CPUs, and the fact that SRCU now maintains per-CPU callback lists. Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
2017-04-12doc: Synchronous RCU grace periods are now legal throughout bootPaul E. McKenney1-34/+47
This commit updates the "Early Boot" section of the RCU requirements to describe how synchronous RCU grace periods are now legal throughout the boot process. Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
2017-01-15doc: Fix RCU requirements typosTetsuo Handa1-6/+6
Signed-off-by: Tetsuo Handa <penguin-kernel@I-love.SAKURA.ne.jp> Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com> Reviewed-by: Josh Triplett <josh@joshtriplett.org>
2016-11-14documentation: Present updated RCU guaranteePaul E. McKenney1-1/+24
Recent memory-model work deduces the relationships of RCU read-side critical sections and grace periods based on the relationships of accesses within a critical section and accesses preceding and following the grace period. This commit therefore adds this viewpoint. Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
2016-08-22documentation: Record reason for rcu_head two-byte alignmentPaul E. McKenney1-0/+22
There is an assertion in __call_rcu() that checks only the bottom bit of the rcu_head pointer, rather than the bottom two (as might be expected for 32-bit systems) or the bottom three (as might be expected for 64-bit systems). This choice might be a bit surprising in these days of ubiquitous 32-bit and 64-bit systems. This commit therefore records the reason for this odd alignment check, namely that m68k guarantees only two-byte alignment despite being a 32-bit architectures. Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
2016-06-15documentation: Add RCU_NONIDLE() restrictions to requirementsPaul E. McKenney1-0/+35
Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
2016-03-31documentation: Emphasize the call_rcu() is illegal from idlePaul E. McKenney1-1/+1
Although call_rcu()'s fastpath works just fine on an idle CPU, some branches of the slowpath invoke the scheduler, which uses RCU. Therefore, this commit emphasizes the fact that call_rcu() must not be invoked from an idle CPU. Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
2016-03-31documentation: Sharpen up the no-readers quick quizPaul E. McKenney1-5/+8
Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
2016-03-31documentation: Get rid of duplicate .htmlx filePaul E. McKenney1-461/+428
This commit uses colors to obscure the quick-quiz answers, thus getting rid of the .htmlx file. Use your mouse to select the answer in order to see the text. Alternatively, use your favorite scripting language to remove all occurences of "<font color="ffffff">" from the file. Reported-by: Linus Torvalds <torvalds@linux-foundation.org> Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
2016-03-31documentation: Remove unnecessary images from requirementsPaul E. McKenney1-8/+20
This commit removes a cutesy cartoon and also a diagram that can just as easily be represented by text. Reported-by: Linus Torvalds <torvalds@linux-foundation.org> Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
2016-03-31documentation: Document illegality of call_rcu() from offline CPUsPaul E. McKenney1-1/+2
There is already a blanket statement about no member of RCU's API being legal from an offline CPU, but add an explicit note where it states that it is illegal to invoke call_rcu() from an NMI handler. Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
2016-03-31documentation: Explain why rcu_read_lock() needs no barrier()Paul E. McKenney1-43/+87
This commit adds a Quick Quiz whose answer explains why the compiler code reordering enabled by CONFIG_PREEMPT=n's empty rcu_read_lock() and rcu_read_unlock() functions does not hinder RCU's ability to figure out which RCU read-side critical sections have completed and not. Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
2016-03-31documentation: Add synchronize_rcu_mult() to the requirementsPaul E. McKenney1-0/+92
Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
2016-03-31documentation: Add real-time requirements from CPU-bound workloadsPaul E. McKenney1-1/+9
This commit records RCU's responsibility to avoid degrading latencies of CPUs running tight loops within properly configured workloads, both in kernel and in userspace. Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
2015-12-05documentation: Update RCU requirements based on expedited changesPaul E. McKenney1-2/+10
Because RCU-sched expedited grace periods now use IPIs and interact with rcu_read_unlock(), it is no longer sufficient to disable preemption across RCU read-side critical sections that acquire and hold scheduler locks. It is now necessary to instead disable interrupts. This commit documents this change. Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
2015-12-05documentation: Clarify RCU memory barriers and requirementsPaul E. McKenney1-27/+39
The RCU requirements do not make it absolutely clear that the memory-barrier requirements are not intended to replace the fundamental requirement that all pre-existing RCU readers complete before a grace period completes. This commit therefore pulls the memory-barrier requirements into a separate section and explicitly calls out the relationship between the memory-barrier requirements and the fundamental requirement. Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
2015-12-05documentation: Expand on scheduler/RCU deadlock requirementsPaul E. McKenney1-5/+9
This commit adds a second option for avoiding scheduler/RCU deadlocks, namely that preemption be disabled across the entire RCU read-side critical section in question. Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
2015-12-05documentation: Composability analogiesPaul E. McKenney1-0/+8
This commit expands on RCU's composability by comparing it to that of transactional memory and of locking. Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
2015-12-05documentation: Cover requirements controlling stall warningsPaul E. McKenney1-1/+24
This commit adds verbiage on boot and sysfs parameters that can be used to control RCU CPU stall warnings, both to change the timeout and to suppress these warnings entirely. Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
2015-12-05Documentation: Record bottom-bit-zero guarantee for ->nextPaul E. McKenney1-0/+43
This commit records RCU's guarantee that the bottom bit of the rcu_head structure's ->next field will remain zero for callbacks posted via call_rcu(), but not necessarily for <tt>kfree_rcu()</tt> or some possible future call_rcu_lazy() variant that might one day be created for energy-efficiency purposese. Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com> [ paulmck: Updates URLs as suggested by Josh Triplett. ]
2015-12-05documentation: Record RCU requirementsPaul E. McKenney1-0/+2799
This commit adds RCU requirements as published in a 2015 LWN series. Bringing these requirements in-tree allows them to be updated as changes are discovered. Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com> [ paulmck: Updates to charset and URLs as suggested by Josh Triplett. ]
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